1. Field of the Invention
This invention relates to the field of providing organic polymer coatings on metal surfaces, and more particularly to the field of utilizing sol-gel films as an interface which promotes adhesion between a metal surface and an organic polymer coating.
2. Technical Background
The use of a sol-gel film to produce a metal surface coating suitable as an interface to improve adhesion between the metal surface and an organic matrix resin or adhesive is well known. The sol-gel film provides corrosion resistance to a limited extent and promotes adhesion with an organic resin. A sol is used to produce the sol-gel film on the surface of the metal. Examples of sols which have been used to produce a sol-gel coating on a metal surface include organosilane coupling agents. The sol-gel film is typically applied by immersing, spraying or drenching the metal in or with the sol without rinsing. The sol-gel film includes sites which bond with the metal and separate sites which can bond with an organic resin coating. After application, the sol coating is usually dried such as ambient temperature or, more commonly, at a temperature between ambient and 250.degree. F. (about 120.degree. C.) to complete the sol-gel film formation. Conventional methods of forming a sol-gel film on a metal surface involve the interaction of metal alkoxides with a metal oxide on the surface of the metal to form M.sub.1 --O--M.sub.2, linkages, in which M.sub.1 is a metal atom on the surface of the metal which is to be coated, and M.sub.2 is a metal atom of a metal alkoxide in the sol. Sol-gel films have been successfully employed as an interfacial layer to promote adhesion between an organic resin and a metal surface. However, useful results have been limited to metals which develop a metal oxide surface, such as aluminum and titanium. Sol-gel films have not been successfully employed as an interfacial layer for promoting good adhesion between an organic polymer coating and the surface of a metal which does not develop a metal oxide surface. Examples of such metals include various noble metals, such as gold, silver, platinum, palladium, iridium, rhenium, ruthenium and osmium.
Therefore, it would be desirable to provide an improved method for forming a sol-gel film on the surface of a metal to promote good adhesion between the surface of the metal and an organic resin coating, especially between an unreactive metal surface, such as the surface of a noble metal, and an organic resin coating.